According to the latest installment in the ongoing saga over the king of dinosaurs' dietary habits, Tyrannosaurus rex was not simply an oversize scavenger. By the time T. rex was lucky enough to find a carcass, smaller animals would have stripped it to the bone first, claims a new study of the giant dino's fierce competition for rotting flesh.

The Jan. 26 study in Proceedings of the Royal Society B doesn't explore what T. rex hunted, but it counters earlier research that suggested the creature could survive only on carrion when it roamed North America some 65 million years ago.

"This has been a discussion for as long as we've known about [T. rex's] existence," said study co-author and ecologist Chris Carbone of the Institute of Zoology in London. "Some people say it's a settled issue, that it both scavenged and hunted, but evidence is scarce and we see both extremes in behavior in large carnivores today."

Adult tyrannosaurs were about 40 feet long, 15 feet high and weighed between 5 and 7 tons, making them one of the largest land-based carnivores ever. However, they shared features common to both full-time scavengers and predators, causing debate about how they subsisted.

Powerful jaws, impact-resistant teeth and huge size are all associated with predatory behavior. An enhanced sense of smell, small eyes and puny forelimbs are associated with scavenging. Previous studies tallied up T. rex's energy costs, determining that a Serengeti-like environment could support one 7-ton toothy beast on carcasses alone.

But that research took too narrow a view of dinosaur life, counting how many calories T. rex needed but not the competition it faced in getting them, said Carbone.

"In that study they essentially fed T. rex carrion hamburgers at a regular interval, which resolved the question of energy intake," he said. "The approach was good, but it was in isolation. We found this argument breaks down quickly in an ecological context."

To see if T. rex could survive on a carrion diet, Carbone's team developed a computer model that merged dinosaur abundance, based on fossils found in the same formations as T. rex, with modern Serengeti scavenging data. Because predator-to-prey ratios in the fossil record are similar to ratio in Africa's scavenger-filled savannas, Carbone said the Serengeti was a good model to bring all of the dinosaur abundance and territory data into perspective.

They concluded that T. rex would have faced such fierce competition from smaller scavenging dinos, that carrion alone wouldn't suffice as a primary food source.

"I never really bought the 'it was only a scavenger' arguments. They treated T. rex in an ecological vacuum with no other animals around," said evolutionary biologist John Hutchinson of the Royal Veterinary College, who was not involved in the study. "This paper puts [T. rex] in the realistic context of a complex environment."

Assuming T. rex could cover about one square mile of territory every day, it would find a 25-ton sauropod carcass once every 5 years, a triceratops-sized carcass once a year and a horse-sized carcass once every 2 months. Even an adult-human–sized carcass would be found only every 6 days to stumble across.

"Just about any carnivore will eat carrion if it encounters it, so there could not have possibly been enough around for a tyrannosaur to subsist on," said paleontologist and evolutionary biologist Martin Sander of Germany's University of Bonn, who was not involved in the study. "They would have been outnumbered by smaller, more abundant scavengers."

If T. rex did compete with tiny-yet-formidable scavengers, it would need to sniff carcasses from about 2 miles away and traverse at least 80 miles per day. Applying the dinosaur's most generous top speed estimate (about 45 mph), that would add up to nearly 2 hours of sprinting to cover that distance.

However, paleontologist Jack Horner of Montana State University, who was not involved in the study and has supported the idea of T. rex as a full-time scavenger, says Carbone's study is interesting but flawed.

Horner said the dinosaurs included in the study cover a time span far beyond when T. rex was certain to have lived, and that his unpublished data contradict assumptions on the abundance of T. rex's competitors. "If their numbers were correct, I would agree with the paper. But I have numbers to suggest they're not," he said.

Horner could not yet share his specific results, as he didn't want to compromise his team's forthcoming publication in the journal PLoS One.

In whatever way Horner's work proves to impact Carbone's interpretations, Carbone said it will all be part of the process of science.

"We made our best argument, which I think firmly rejects the idea that T. rex was a scavenger. If there's new evidence to suggest otherwise, I'd love to take a look at it," Carbone said. "We've just got to wait and see what [Horner] has got."

In the meantime, Carbone said he'd like to go after a "million-dollar question" surrounding T. rex.

"What did it hunt, and how?" he said. "There are different answers in different fields. We need to bring these groups together, I think, to understand what T. rex was like as a hunter."

Images: 1) Fossilized skeleton of Tyrannosaurus rex./Flickr/Chealion. 2) The predicted relative abundance of predators, by mass, that may have competed with T. rex for food (top) and the predicted relative abundances of herbivores that would have made up the majority of carcasses (bottom)./Proceedings B/C. Carbone.

The mysterious, spectacular flare of Comet 17P/Holmes has been observed three times, and it may give warning of an imminent explosion fueled by carbon monoxide gas when it returns in 2014, say astronomers.

Holmes shocked the world in October 2007 when it suddenly brightened by a factor of 500,000, going from a humdrum ball of dust to a brilliant orb visible to the naked eye. The comet spewed 100 million tons of dust into space, comparable to the amount of ash unleashed by Mount St. Helens, and briefly swelled to a diameter greater than the sun's.

But despite months of observations from hundreds of telescopes, the cause of Holmes' dramatic explosion remains unknown.

Astronomers initially suggested that a dusty crust may have formed on the comet's nucleus as it approached the sun, trapping frozen ice underneath. As it neared the sun, the surface would heat so rapidly that the ice turned from solid to gas without even melting. Gas would build up and burst through the crust, sending Holmes' innards flying outward.

But what was the fuel? The most obvious source inside the comet was sloshy, amorphous water ice crystallizing into ordered, snowflake-like filaments, a process that gives off heat. But a pair of Polish researchers showed that energy from crystallizing water ice wouldn't be enough to drive such a huge explosion.

Now, the same team suggests a new fuel: carbon monoxide gas. In an upcoming paper in the journal Icarus, geophysicists Konrad Kossacki of the Warsaw University and Slawomira Szutowicz of the Polish Academy of Sciences report they ran simulations to show that carbon monoxide gas inside the comet nucleus could reach pressures of 10 kilopascals [100 millibars, or 1.45 psi], the same difference in pressure as climbing from sea level to 3,280 feet. This would be enough pressure to make the comet's fragile core erupt, they say.

Comet Holmes has actually exploded twice before, when it was discovered in 1892 and again in 1893. All three outbursts happened about 200 days after the comet's closest approach to the sun, which could provide some clues as to how much heat the core needs to explode — and whether it might explode again during its next visit in 2014.

"You must remember this," Sam the piano player crooned to Humphrey Bogart and Ingrid Bergman in Casablanca. The couple might have recalled even more about their days in Paris if they'd been napping when Sam played the tune again.

Replaying memories while people are awake leaves their memories subject to tinkering. But reactivating memories during sleep protects them from interference, researchers in Germany and Switzerland report online January 23 in Nature Neuroscience.

The finding shows that the brain handles memories differently during sleep than while awake, says Sara Mednick, a cognitive neuroscientist at the University of California, San Diego who was not involved in the research. Armed with this new knowledge, she says, therapists may be able to destabilize traumatic memories and overwrite the bad memories with good ones, then solidify the new memory with a nap.

In the new study, volunteers played a Concentration-type game in which they had to remember the locations of pairs of cards. Meanwhile, a mask wafted a slightly unpleasant odor into the volunteers' nostrils. Once the volunteers had mastered the game, some stayed awake while others took about a 40-minute nap. Researchers reactivated the memory in some volunteers by releasing the odor again. After the nappers woke up, the volunteers played a slightly different version of the card game and were tested to see how well they recalled the locations of the original cards.

Both sleeping and awake volunteers who didn't have their memories jogged by the odor remembered about 60 percent of the pairs. When researchers triggered memory reactivation while volunteers were awake, recall of the correct locations dropped to about 41 percent. The researchers had expected that result. Previous studies have shown that replaying a memory while awake makes it vulnerable to interference from new material, such as from the second card game.

But the real surprise came when the team replayed memories in the sleeping volunteers and checked how that affected their waking performance. "With odor reactivation, they were almost perfect," says coauthor Susanne Diekelmann, a psychologist and neuroscientist at the University of Lübeck in Germany. Volunteers correctly picked out about 84 percent of the original card pairs when the memory replayed during a nap that consisted mostly of deep slow-wave sleep (volunteers were woken up before they entered rapid eye movement, or REM, sleep).

Brain scans also revealed that different areas of the brain were involved during memory replay depending on whether the volunteers were awake or asleep. While awake, replaying the memory triggered activity mostly in the right lateral prefrontal cortex, a part of the brain involved in memory recall. But during sleep, memory replay was associated with strong activity in the hippocampus and parts of the cortex. The hippocampus is involved in memory formation, and memories are transferred from short-term memory in the hippocampus to long-term memory in the cortex. Reactivating memories during sleep may speed the transfer, Diekelmann says.

The researchers are now testing whether replaying memories during REM will also stabilize them. Brain activity during that sleep state is similar to that while awake, so the researchers suspect memories may become unstable during REM to allow for editing and reorganization.

A massive star is caught fleeing its former companion, careening through space behind a brilliant yellow arc of gas and dust, in this exquisite new image from NASA's Wide-Field Infrared Survey Explorer telescope.

Named Zeta Ophiuchi, the bright blue star in the image's center is about 20 times more massive than our sun. Were it not shrouded by dust, it would be one of the brightest stars in the sky — yet long ago, it orbited an even more massive star.

When that star exploded in a supernova, Zeta Ophiuchi took off like a shot. When WISE caught it, Zeta Ophiuchi was flying at 54,000 miles per hour.

As it plows through space, the star's powerful winds shove gas and dust out of its way into a bow shock, much like a boat's prow displaces water. Although this bright arc is hidden in visible light, matter in the shock is so compressed that it heats up and glows in wavelengths visible to WISE's infrared eyes.

The picture was generated by combining 16 individual exposures, which were taken between February 27 and March 7, 2010. Blue and cyan coloring in this image represent light emitted at wavelengths of 3.4 and 4.6 micrometers, which is predominantly from stars. Green represents 12-micrometer light and red represents 22-micrometer light, which is mostly emitted by dust.

Zeta Ophiuchi is already about halfway through its 8-million-year lifespan. Like its late partner, it will probably end its life exploding as a supernova.

A federal entomologist has become the latest researcher to voice doubts about neonicotinoids, a controversial new type of pesticide that may be linked to the collapse of honeybee populations in the United States.

Imidacloprid is manufactured by German agrochemical Bayer, who also manufacture clothianidin, another neonicotinoid. Both share a common mechanism of action, and their potential impacts on bees have led many western European countries, including France and Germany, to partially ban neonicotinoids. In 2003, however, the Environmental Protection Agency approved clothianidin for U.S. use.

Since its approval, clothianidin has become widespread. Approiximately $262 million worth was used last year on crops including corn, a pollen-rich favorite of honeybee diets. During this time, honeybee populations have also gone into sharp and as-yet-unexplained decline. Some researchers think a deadly combination of disease and some immune system-weakening stress, such as a pesticide, could be responsible.

Correlation isn't cause, but there are already grounds for concern about clothianidin. In December, leaked memos from EPA scientists described the scientific inadequacy of a key Bayer study used to justify clothianidin's approval.

"Clothianidin's major risk concern is to non-target insects (that is, honey bees)," wrote those researchers. "Exposure through contaminated pollen and nectar and potential toxic effects therefore remain an uncertainty for pollinators."

Pettis' study has not yet been officially published, but the Independent notes that French researchers claim to have replicated the findings in a study published last March in Environmental Microbiology.

"The interaction between [Nosema] and a neonicotinoid (imidacloprid) significantly weakened honeybees," they wrote.

An important portion of the Himalaya's glacier cover is currently stable and, thanks to an insulating layer of debris, may be even growing, a new study finds. The study's conclusion contradicts a portion of the 2007 Intergovernmental Panel on Climate Change report that had to be retracted last year because it could not be substantiated.

Though the IPCC report stated that the risk of the region's glaciers "disappearing by the year 2035 and perhaps sooner is very high," the new study finds that ice cover is stable in the Karakoram mountains, a northern range that holds about half of the Himalaya's store of frozen water.

That's not to imply that water reservoirs on what's often called the roof of the world aren't under stress. Throughout most Himalayan ranges, roughly 65 percent of the studied glaciers were shrinking, Dirk Scherler of the University of Potsdam, Germany, and his colleagues report in the January 23 Nature Geoscience. But in Karakoram, 58 percent of studied glaciers were stable or slowly expanding up to 12 meters per year.

Scherler's team pored over satellite images of 286 glaciers throughout the Himalayas. Collected between 2000 and 2008, they showed a consistent trend everywhere except the Karakoram: a reduction in the area of glacial cover. Many glaciers in those regions also were stagnant — not flowing — which, Scherler says, is an indicator of poor health.

The new findings are consistent with what Kenneth Hewitt of Wilfrid Laurier University in Waterloo, Ontario, has observed, and point to the fact "that the picture of climate change effects in high Asia is much more complicated than most people realize."

Indeed, for much of the past century Karakoram's glaciers were in retreat. A 2005 paper by Hewitt described a turnaround that commenced only in the late 1990s.

In the new study, Scherler's team looked for factors that might affect the responsiveness of Himalayan glaciers to regional warming. A rocky blanket quickly emerged as a major one.

In general, the warmer the air above a glacier becomes the faster exposed ice will melt. A thin veneer of dust or grit will darken glaciers, increasing the amount of heat they absorb and exaggerating their warming, much as a dark roof becomes hotter in sunlight than a light gray one. But once the depth of any rock cover exceeds several centimeters, it will insulate ice from the sun's warming rays. In some lower reaches of Himalayan glaciers, especially in the Karakoram, rock debris can include house-size boulders, Scherler observes.

In this range, it seems, rocky rubble eroded from uphill peaks serves to decouple the effects of regional warming from glacial retreats. The new analysis found retreat rates varied in the Himalaya "from high for debris-free glaciers to zero for glaciers with debris cover greater than 20 percent."

What the satellite data, which surveys the extent of a glacier's coverage, can't establish is how much area glaciers might be thinning. Such information requires ground measurements, Hewitt says, which are particularly rare in this part of the world. But they could also prove quite crucial. He notes that some data emerging from India and China suggest that the diffuse fallout of soot from local industries, traffic and cook stoves might be subtly darkening debris-free portions of Himalayan glaciers — and constitute "a more significant factor than even temperature change in their melting."

Image: A glacier in the Karakoram mountain range./Flickr/Guilhem Vellut